More from WebMD

Sept. 21, 2010 -- Yearly flu shots may do more than stave off the seasonal flu -- they may also prevent heart attacks, according to a new study in the Canadian Medical Association Journal. And the earlier you get the flu shot, the greater this protection, the study shows.

"If substantiated, this finding has implications for timely supply and administration of influenza vaccine and could lead to changes in recommendations for timing of vaccination," concludes A. Niroshan Siriwardena, PhD of the University of Lincoln in the U.K.

Heart attack risk tends to rise in the winter months, just like the flu, suggesting a link between the two conditions. Exactly how the flu shot may protect against first heart attack is not clear, but infection could somehow trigger plaque rupture in the arteries, resulting in a heart attack or stroke, the researchers suggest.

The new study included 16,012 people who had a heart attack between Nov. 1, 2001 and May 31, 2007, and 62,694 sex- and age-matched people who did not have heart attacks. Those who got their flu shot during the past year had a 19% reduced risk for heart attack, compared with their counterparts who did not get a flu shot that year.

The earlier in the flu season that participants got the flu shot, the lower their risk for first heart attack, the study showed. By contrast, the pneumonia vaccine did not provide protection against heart attack.

Inflammation May Play a Role

"Heart attacks increase during the winter time, and we think that the fact that there are more infections during the winter may be one of the reasons," says Stephen Nicholls, MD, PhD, a cardiologist at the Cleveland Clinic in Ohio.

"The findings of the current study are interesting and important," he tells WebMD. "If you get the flu vaccine, and get it early, you are less likely to get the flu and less likely to have a heart attack."

"If you have plaque that builds up in your artery walls and you get a viral infection, you do tend to have more inflammation, and when a plaque becomes inflamed, it's more likely to rupture and cause a heart attack," he says.

CDC Calls for Universal Flu Vaccines

"This is a first year that the federal Centers for Disease Control and Prevention recommends universal flu vaccination [for all people 6 months of age and older], and there are many benefits to this in terms of preventing the flu, and we might be able to prevent some heart attacks too," says Phil Smith, MD, chief of infectious disease at the University of Nebraska Medical Center in Omaha.

While the study showed the earlier the better, it is never too late to get the flu shot, he stresses.

"The official flu season is September through March, but the flu tends to peak in December, January, and February," he says.

"It is never too early or too late to get vaccinated," Smith says. There was a shortage of vaccines last year, but this year, most doctors and other outlets have already received their supply.